fixed trusty build (#682)

* fixed trusty build (g2o backward compatibility)

docker/trusty/Dockerfile

@@ -0,0 +1,28 @@
+# Image: introlab3it/rtabmap:trusty
+
+FROM ros:indigo-perception
+
+# Install/build dependencies
+RUN apt-get update && \
+    apt-get install -y ros-indigo-rtabmap-ros && \
+    apt-get remove -y ros-indigo-rtabmap && \
+    rm -rf /var/lib/apt/lists/
+
+WORKDIR /root/
+
+# Clone source code
+ARG CACHE_DATE=2016-01-01
+RUN git clone https://github.com/introlab/rtabmap.git
+
+RUN rm /bin/sh && ln -s /bin/bash /bin/sh
+
+# Build RTAB-Map project
+RUN source /ros_entrypoint.sh && \
+    cd rtabmap/build && \
+    cmake .. && \
+    make && \
+    make install && \
+    cd ../.. && \
+    rm -rf rtabmap && \
+    ldconfig
+